Dan Ruggirello wrote:
Paul,
Here are the normal modes results for the MMP. Not sure I modeled the
aft mount very accurately
though. It is fixed in X,Y,Z and free to rotate in RX,RY,RZ. You
mentioned that the Questair is
only fixed vertically though. I could go ahead and release the X and
Z directions and see how it
behaves - let me know your opinion.
The mass I used was 265 lbs for the remaining engine and it is at 8"
behind the MMP. The
PSRU/prop mass is 70 lbs and 6" in front of the MMP.
The mpeg file names specify mode number and frequency. The first
three modes are from the barry
mounts, 10hz, 13hz and 64hz. The last two modes are psru/prop/MMP
modes. The 118 hz mode is the
psru/prop bending mode against the MMP, and the 143hz mode is the
prop/psru moving against the
MMP.
So, if the model is correct, you wouldn't want to operate the engine
or prop continuosly near 1100
rpm (118 hz) or 1370 rpm (143 hz) (ideally we would slap a few
accelerometers on and gather some
test data). But, if the rear mount were free in Z, you will likely
see a small frequency increase
in the 118 HZ mode and a larger increase for the 143 Hz which means
moving closer to the common
operating frequencies. Also, the MMP geometry in this model is a bit
different than what was
tested - much different than what is being built?
Sorry if the mpeg files are too fast, I can't figure out how to slow
it down. If you set your
mpeg viewer to repeat you can get an idea of what the mode is doing
though.
Next step would be to put a sine prop force and/or peak engine torque
at the operating rpm's to
see how the applied loads excites the last two frequencies.
I would like to take a look at the ultimate bell housing eventually to
see how it compares. Can
you export two IGES files - a solid and surface model?
Also, I looked at the other redrive design you sent. How expensive do
you suppose it would be to
get one built? How about the weight? I would change the housing in
that design to something like
the ultimate bell housing though instead of using struts. It would be
easier to install and maybe
stiffer in torsion.
Dan